DESCRIPTION (Investigator's Abstract): Changes in human vision throughout the can be attributed are now beginning to be understood. It is known that the intensity and spectral composition of the retinal stimulus changes over the life span due to age-related increases in ocular media absorption. The sensitivities of the cone receptors continuously decline from age 10 through adulthood. These changes in pre-receptoral and receptoral processing will necessarily alter the input to post-receptoral processes subserving color appearance. The purpose of this research is to study post-receptoral processing of chromatic and achromatic information throughout the life span, with emphasis on the elderly (60-80 years). Test conditions will be used that allow the separation of pre-receptoral, receptoral and post-receptoral mechanisms. Color discrimination will be measured under two conditions; one that depends on variation only in short-wave cone activity and one in which short-wave cones do not contribute to color discrimination. These data will indicate whether age-related changes in chromatic discrimination are due to selective loss in one particular pathway. To determine relative age-related changes in chromatic and achromatic pathways, opponent-chromatic response functions, saturation-scaling, and brightness-matching functions will be measured. These data will not only document age-correlated changes in individual mechanisms, but will also be used to test models of the relations between processing at different levels, particular wavelength discrimination. All of the psychophysical tests will include observers ranging in age from 10 to 80 years. Complete psychophysical functions will generally be measured for a group of 10 observers and selected spectral points will be measured for an additional 30-40 observers. Psychophysical testing will also be carried out with pseudophakic patients having intra-ocular lens implants that either transmit or absorb ultraviolet radiation to further test the hypothesis that ultraviolet light exposure contributes to age-correlated changes in short-wave cone sensitivity, and hence attenuates inputs to post-receptoral processes. These data may reveal an important environmental contribution (light itself) to individual differences in aging. Since light exposure can be partially controlled, the data may have public health significance for aging populations. This research is thus concerned with separating the optical and neural mechanisms that mediate age-correlated changes in the perception and processing of color. These studies may contribute to our understanding of the factors that contribute to individual variation in aging of the human visual system.